Projects

Imaging of the inner ear in relation to cochlear implants

Johan Frijns

Potential CI candidates are scanned preoperatively by CT and MRI scanner to assess the anatomy and detect possible abnormalities. Imaging helps to predict the expected difficulty of the surgery and the additional risks and also supports the choice of the type of implant. Patients are normally scanned on a scanner with a magnetic field strength of 1.5 or 3 Tesla. Recently, there has been an MR scanner came with a magnetic field strength of 7 Tesla on the market, but this scanner is almost only used for research purposes.

Scanning with a 7 Tesla scanner is expected to provide more details because of the improved resolution. This is very relevant for scanning inner ears because of its many very delicate. With this research we aim to explore the possibility of scanning inner ears with the hypothesis that this yields a more accurate representation of the anatomical structures of the inner ear. A group of 13 CI candidates preoperatively both 3T and 7T undergo MRI scans, and the resulting images of both modalities were evaluated and compared by two experienced radiologists with expertise in the field of head and neck imaging. A list of the 24 anatomical structures have been assessed on the quality of display and compared between the two scanners. The results of this study showed that, in particular, improved the smallest structures become visible with the 7 Tesla scanner. However, part of the 7 Tesla scans exhibit artifacts that affect the quality of the scans. The latter is the reason to further optimize the protocol.

Our group has a long-standing research line in CT-imaging in relation to cochlear implants, in close collaboration with the department of Neuroradiology (dr. Berit Verbist, prof. Marc van Buchem). Research interests have evolved from the development of imaging protocols and defining standards for the documentation of ,e.g., insertion depth to relating electrode design and intracochlear position to functional outcome measures, such as speech perception and insertion trauma. The imaging data also serve as input for the psychophysical experiments and computational modeling. At present we are evaluating the additional value of fusion of pre-operative (3T and 7T) MRI images with post-operative low-dose CT-scans.